Active Late Cenozoic Flexures in the Precordillera in Northern Chile: Correlations With the Shallow Seismic Activity, and Implications for the Uplift of the Altiplano

The western slope of the Altiplano, in Northern Chile, is characterized by the existence of west-vergent thrust-systems. In the study region (Aroma area, 19 °25'S-19°45'S), three N25°W-trending flexures related to the activity of west-vergent thrust-faults were mapped. In the core of one of these flexures, a N25°W oriented blind thrust-fault dipping 45° to the East cuts through the Paleozoic basement, but not through the Cenozoic cover. The activity along the thrust-system controlled deposition of Miocene sediments and volcanoclastics, and deformed them. The minimum vertical throw associated with the flexure-system is approximately 1,000 m. A N5°E-trending, subvertical transcurrent-fault cutting Recent coluvial deposits, is associated with the shallow earthquake occurred on July 24, 2001 (Mw=6.3). In the north part of the study region, several landslides formed at the front of a W-NW-trending south-vergent thrust-fault. This structure is a transfer-fault between two of the flexures and it is still active. To the north, we correlate the described flexure-system, to the Moquella Flexure (Camiña valley), and at the latitude of Arica, to the Ausipar Thrust-fault and the Oxaya Anticline. To the south, it can be correlated to the Altos de Pica west-vergent thrust-system (latitude of Iquique). The west-vergent thrust-fault system along the Precordillera is, at least, 300 km long, is still active, can be followed in southern Perú, and accommodates the uplift of the western part of the Altiplano in this region.